Azimuthal separation in nearly back-to-back jet topologies in inclusive 2- and 3-jet events in pp collisions at sqrt(s) = 13 TeV

A measurement for inclusive 2- and 3-jet eventsof the azimuthal correlation between the two jets with thelargest transverse momenta,Δφ12, is presented. The mea-surement considers events where the two leading jets arenearly collinear (“back-to-back”) in the transverse plane andis performed for several ranges of the leading jet transversemomentum. Proton-proton collision data collected with theCMS experiment at a center-of-mass energy of 13 TeV andcorresponding to an integrated luminosity of 35.9fb−1areused. Predictions based on calculations using matrix ele-ments at leading-order and next-to-leading-order accuracy inperturbative quantum chromodynamics supplemented withleading-log parton showers and hadronization are generallyin agreement with the measurements. Discrepancies betweenthe measurement and theoretical predictions are as large as15%, mainly in the region 177◦<180◦. The 2- and3-jet measurements are not simultaneously described by any of models.